a. Field of the Invention
The instant invention relates generally to the navigation of a medical device through a patient. More specifically, the instant invention relates to a method and system for detecting the movement of a reference point utilized in a non-ionizing localization system, such as is often employed in navigating a medical device through a patient, and mitigating the effects of such reference point movement.
b. Background Art
It is well known to generate heart chamber geometry in preparation for cardiac diagnostic or therapeutic procedures. Often, a mapping catheter tip is placed within the heart chamber and/or against the wall of the heart chamber and the three-dimensional coordinates of the mapping catheter tip are measured using a localization system. The three-dimensional coordinates become a geometry point. Multiple measurements are taken as the mapping catheter is moved within the heart chamber, resulting in a cloud of geometry points (also referred to as “location data points”) that defines the geometry of the heart chamber. Various surface construction algorithms may then be applied to wrap a surface around the cloud of geometry points to obtain a three-dimensional representation of the heart chamber geometry.
It is desirable for the three-dimensional coordinate system relative to which the geometry points are measured to have a stable reference point or origin. This stable reference point or origin is referred to herein as a “navigational reference” for the localization system. While any stable position will suffice, it is desirable for many reasons to utilize a navigational reference that is proximate to the mapping catheter. Thus, a catheter-mounted reference localization element is often inserted into the heart and positioned in a fixed location, such as the coronary sinus, to establish the origin of the coordinate system relative to which the location of the mapping catheter will be measured.
It is known, however, that the navigational reference may become dislodged. For example, the mapping catheter may collide or become entangled with the catheter carrying the navigational reference (referred to herein as the “reference catheter”), or the practitioner moving the mapping catheter may inadvertently jostle the reference catheter. The navigational reference may also be dislodged by patient movement. Other factors, such as patient hydration and respiration, may make it appear as if the navigational reference has become dislodged when, in fact, it has not become dislodged.
When the navigational reference becomes dislodged, it effectively shifts the origin of the coordinate system used by the localization system. Unless the dislodgement is detected and accounted for, positions of the mapping catheter measured after the dislodgement will be invalid.